1. Field
The present disclosure relates to rubber compositions intended in particular for the manufacture of tires or semi-finished products for tires, in particular rubber compositions exhibiting a high stiffness.
2. Description of Related Art
It is known to use, in some parts of the tires, rubber compositions exhibiting a high stiffness during small strains of the tire (cf. WO 02/10269). Resistance to small strains is one of the properties which a tire has to exhibit in order to respond to the stresses to which it is subjected.
This stiffening can be obtained by increasing the content of reinforcing filler or by incorporating certain reinforcing resins in the constituent rubber compositions of the parts of the tire.
However, in a known way, the increase in the stiffness of a rubber composition by increasing the content of filler can be disadvantageous to the hysteresis properties and thus rolling resistance properties of the tires. In point of fact, it is an ongoing aim to lower the rolling resistance of tires in order to reduce the consumption of fuel, for economic and environmental purposes.
Conventionally, this increase in the stiffness is obtained by incorporating reinforcing resins based on a methylene acceptor/donor system. The terms “methylene acceptor” and “methylene donor” are well-known to a person skilled in the art and are widely used to denote compounds capable of reacting together to generate, by condensation, a three-dimensional reinforcing resin which will become superimposed and interpenetrated with the reinforcing filler/elastomer network, on the one hand, and with the elastomer/sulphur network, on the other hand (if the crosslinking agent is sulphur). The methylene acceptor described above is combined with a hardener, capable of crosslinking or curing it, also commonly known as “methylene donor”. Crosslinking of the resin is then brought about during the curing of the rubber matrix by formation of methylene bridges (—CH2—) between the carbons in the ortho and/or para positions of the phenolic nuclei of the resin and the methylene donor, thus creating a three-dimensional resin network.
The methylene donors conventionally used in rubber compositions for tires are hexamethylenetetramine (abbreviated to HMT) or hexamethoxymethylmelamine (abbreviated to HMMM or H3M) or hexaethoxymethylmelamine.
However, it is desirable to find alternatives to the conventional reinforcing resins.
Previously, the Applicant Companies have discovered, during their research studies, that the normal reinforcing resins can advantageously be replaced by an epoxy resin with a diamine as hardener. The use of this pair of epoxy resin and diamine reactants makes it possible to obtain rubber compositions exhibiting a greater low-strain stiffness, in comparison with conventional rubber compositions, without significantly damaging the hysteresis, as described in the document FR 2 951 182.